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The present invention relates to wall mountable electrically activated fumigation devices. It provides devices with improved electrical efficiency and shut-off protection.
Devices are known for fumigating an enclosed area, such as a room in a house, by expelling a fumigant (e.g. typically an insecticide or fragrance) upon an application of heat. As disclosed in U.S. Pat. No. 5,796,914, some of these devices include a disposable canister containing the fumigant, and an electric heater positioned under the fumigant. When activated the device produces a fog that is expelled out to fumigate a room or the like.
Before the application of heat, the fumigant typically is in a solid form. It subsequently transforms into a viscous gel material in response to the initial introduction of heat. Further heating will produce the fog.
U.S. Pat. No. 3,872,280 is an example of an electrically heated vaporizer that also directly plugs into an electrical receptacle. U.S. Pat. Nos. 4,687,904, 4,777,345, and 4,780,286 all provide examples of electrically activated fumigation devices that utilize electricity to set off a charge of insecticide to fumigate a room. These latter devices then automatically disable or otherwise shut off as will be described below.
For example, the U.S. Pat. No. 4,687,904 device uses a positive temperature co-efficient ceramic heater (xe2x80x9cPTC heaterxe2x80x9d) to initiate the fogging. As the insecticide is volatilized, a lead-in wire is fused, interrupting the electrical circuit necessary to power the PTC heater. The fusible lead-in wire is incorporated within the structure of the canister so that the outside portion of the device may be reused by inserting a new canister with its new charge of insecticide and also with its new fusible lead-in wire.
The U.S. Pat. No. 4,777,345 device similarly utilizes the fusing of an electrical lead contained within a replaceable canister as a means of disabling or turning off a fumigating device. However, the wire that is fusible within the canister is itself a resistance heater wire, not a separate PTC heater.
The U.S. Pat. No. 4,780,286 device depends upon a PTC heater to activate a charge within a disposable canister. However, the heat of the reaction does not fuse a fusible lead-in wire. Instead it melts a eutectic metal connector, the loss of which again interrupts the electrical circuit to the PTC heater. Other devices of interest are described in U.S. Pat. Nos. 5,402,517, 5,095,647, 4,425,302, and 2,513,919.
While the above devices, and particularly U.S. Pat. No. 5,796,914, have been effective in controlling insects within confined spaces (or otherwise dispersing other desired volatiles such as fragrances and disinfectants), there is a continuing desire to focus the heat generated by the heating element at a particular location adjacent the material being heated, without significant heating of the outer casing. Further, it is desired to provide redundancy in the manner of shutting off the fumigator once it has started (to reduce incidence of overheating), and to provide protection against spilling if the device is mounted upside down in the wall socket.
In one aspect the invention provides an electric fumigation device having an outer housing, an electrical plug extending from the outer housing, and a well mounted in the outer housing. The well has a well mouth that can open to the atmosphere and an outwardly open recess in a lower portion of a wall of the well, the well containing a heat-activatable fumigant. There is also a heater at least partially enclosed in the recess for heating the heat-activatable fumigant in response to electricity delivered via the electrical plug.
In preferred forms there is a eutectic thermal cut-off device (xe2x80x9cTCOxe2x80x9d) that activates to automatically disable the heater at a predetermined temperature, and the outwardly open recess is downwardly open. In addition, the heater can itself create an open circuit when the heater reaches a predetermined temperature (if the TCO hasn""t worked before then).
If the fumigating device is plugged in upside down the TCO will cause the dispenser to self-disable before the active ingredient is dispensed from the well. This is because the steel well will largely retain the heat of the heater near the recess long enough to trigger the cutoff, rather than immediately transferring the heat along the well to the fumigant which in an upside down positioning would be remote from the heater (such as aluminum might do).
The edges of the recess can be crimped around the heater to assist in retaining the heater in the recess, and walls of the well can be made of tin-coated steel having a thickness of between 0.25 and 0.5 millimeter (a preferred thickness is 0.35 mm). The heater that is placed in the recess can be a resistance heater designed to open (and thus cease to work) after heating to a selected temperature. For example, it can be a resistive film heater housed in a ceramic block.
The fumigant is preferably an insect control agent (e.g. insecticide, insect repellent, or insect growth regulator), a fragrance, and/or a disinfectant. The most preferred fumigant is permethrin. However, a wide variety of synthetic and naturally occurring insecticides would also work.
In another aspect the invention provides a method of fumigating an area having an electrical receptacle mounted on a wall with a fumigant. One provides a device of the above kind, plugs the device into the electrical receptacle, and allows electricity from the electrical receptacle to cause a release of the fumigant. There can also be a further step of disabling the heater when an area between the well and outer housing exceeds a thermal cutoff temperature. In an especially preferred method the device that is used also has a redundant second thermal cutoff.
In yet another form the invention provides a method for constructing such a fumigation device. One obtains a well having an open mouth at a first distal end and a downwardly extending recess in a second distal end. The downwardly extending recess has opposed first and second edges. One inserts a heater element including an upper flange into the downwardly extending recess, bends the opposed edges of the downwardly extending recess under the flange of the heater element, and places a fumigant in the well. One the encloses the mouth of the well with a cover, and electrically couples the heater element to an electrical plug.
The well contains a heat-activatable chemical charge, preferably in the form of pellets containing both an active ingredient and blowing agent for expelling the active ingredient from the well by a self-sustaining chemical reaction. The blowing agent may combust, or be a heat-activatable but non-combusting blowing agent such as azodicarbonamide.
The well mouth can be closed by a cover made of a material sufficiently impervious to water and atmospheric gases so as to be able to protect the chemical charge during storage, but openable by the blowing agent means to release fumigant at the well mouth. To accomplish this function, the cover may be capable of bursting, melting, or otherwise releasing fumigant in response to the temperature or pressure generated by the blowing agent means.
The heater is preferably a resistance heater designed to break or otherwise become discontinuous after heating to a select temperature, thereby interrupting the flow of the electricity through the fumigating device. Various resistance heaters are known to those skilled in the art, including heaters utilizing a loop or a wound coil of resistance wire. Another alternative heating means is a positive temperature co-efficient heater, commonly called a xe2x80x9cPTCxe2x80x9d heater. A positive temperature co-efficient heater may be made self-disabling by selecting its capacity to be such that it burns out and provides an open circuit when a desired temperature is reached.
The most preferred heater is a ceramic encapsulated metal film resistor heater. However, other resistance heaters also are within the breadth and scope of the invention, including wire wound resistors, foil heaters, resistive conductive patterns printed, etched, or otherwise formed on a supporting substrate, and the like.
In addition to employing heaters that break or self-consume, it is possible to provide a TCO selected to interrupt the flow of electricity through the fumigating device when the TCO is heated above a selected maximum temperature. This TCO can be of the xe2x80x9ceutecticxe2x80x9d type so as to disable the heater when temperatures within the fumigating device have risen above a selected maximum temperature.
The invention thus provides an electric fumigator that efficiently uses heat (as the heater directly transfers heat to the well through both its top and sides, reduces the risk of heating the fumigant when the device is plugged in upside down in a possible spill position (as the selection of materials and heater placement activates the safety shutoffxe2x80x94in this case the TCOxe2x80x94before fumigation would begin), minimizes the likelihood of the outer housing becoming too warm (due to the redundant thermal cutoffs), and which is relatively easy to assemble. Moreover, careful selection of the heater and eutectic cutoff can permit the device to be used with a wide variety of voltages, while retaining consistent cutoff.
The foregoing and other advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part thereof, and in which there is shown by way of illustration, and not limitation, a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention. Reference must therefore be made to the claims herein for interpreting the scope of the invention.